Fat is accumulated in the human body in adipocytes, the main sites of fat storage in the body, in the form of triacylglycerol. The lipolytic enzyme triacylglycerol lipase is activated by cyclic adenosine monophosphate (cAMP) and degrades fats into triglycerides and fatty acids.
Caffeine can increase the amount of cAMP by inhibiting the activity of nucleotide phosphodiesterase and, thus, can promote lipolysis by enhancing the activity of triacylglycerol lipase. However, because the solubility of caffeine in water at room temperature is only about 2%, its content in cosmetics is restricted. Even if caffeine could be dissolved, it may be precipitated if the temperature is lowered. Accordingly, its use in cosmetics is limited.
Niacinamide has been used to achieve skin-whitening effect in the field of cosmetics as disclosed in Korean Patent Registration No. 10-0860605 or Korean Patent Publication No. 10-2011-0085544.
The inventors of the present disclosure have made efforts to solve the above-described problem. As a result, they have found out that when caffeine is used together with niacinamide, niacinamide prevents precipitation of caffeine and improves the stability of a solution in which caffeine is dissolved at low temperatures.